DLI (Defense Language Institute): Located in Washington DC, Monterrey, California and Texas. They recruit through usajobs and may advertise under the US military, such as the air force, army, etc. Here's an example of their adverts. Pay is usually $58,000-$75,000 plus benefits.

i-to-i: Trainers usually work on the weekend. You pay i-to-i a certain fee and keep the rest of the fees the students pay.

Oxford Seminars: Trainers usually work on the weekend. You pay Oxford Seminars a certain fee and keep the rest of the fees the students pay.